Dynamic shrimp grader and grading method

ABSTRACT

A dynamic shrimp grader and grading method of universal application to all types of shrimp which in a first embodiment (FIGS. 1-6) utilizes a series of sequential, slightly inclined trays, each hving a number of parallel V-shaped channels with grading slots at their end. The trays are mounted on an upper frame which is driven by an eccentric drive upwardly and simultaneously forwardly with respect to the grader&#39;&#39;s basic support structure, imparting a dynamic action, the upper frame and basic support structure being connected together by a number of angularly disposed, flexible reinforced fiberglass strip springs. Shrimp enter at the top of the grader moving down the channels under the dynamic action of the moving trays and are graded by their width, the smaller falling through the slots in the upper trays, the slot width and length becoming larger from each upper tray to the succeeding lower tray. The shrimp are aligned generally vertically by the sides of the channel and have a tendency to flatten out under the dynamic action of the trays as they progress down the channel (FIG. 8A-8C). The V-shaped channels are formed by means of joining together an alternating series of flat strips (FIG. 5) or alternatively by appropriately bending a single strip (FIGS. 5A). A second embodiment (FIG. 7) utilizes a single flat tray with a staggered series of progressively larger, grading holes therein in place of the trays with the V-shaped channels of the first embodiment.

United States Patent [191 Skrmetta Jan.8,1974

[ DYNAMIC SHRIMP GRADER AND GRADING METHOD [76] Inventor: Raphael Q.Skrmetta, 4610 Press Dr., New Orleans, La. 70126 22 Filed: July 31,1972

21 Appl. No.: 276,391

Primary Examiner-Allen N. Knowles Att0rneyC. Emmett Pugh et al.

[ ABSTRACT A dynamic shrimp grader and grading method of universalapplication to all types of shrimp which in a first embodiment (FIGS.l-6) utilizes a series of sequential, slightly inclined trays, eachhving a number of parallel V-shaped channels with grading slots at theirend. The trays are mounted on an upper frame which is driven by aneccentric drive upwardly and simultaneously forwardly with respect tothe graders basic support structure, imparting a dynamic action, theupper frame and basic support structure being connected together by anumber of angularly disposed, flexible reinforced fiberglass stripsprings. Shrimp enter at the top of the grader moving down the channelsunder the dynamic action of the moving trays and are graded by theirwidth, the smaller falling through the slots in the upper trays, theslot width and length becoming larger from each upper tray to thesucceeding lower tray. The shrimp are aligned generally vertically bythe sides of the channel and have a tendency to flatten out under thedynamic action of the trays as they progress down the channel (FIG.8A-8C). The V-shaped channels are formed by means of joining together analternating series of flat strips (FIG. 5) or alternatively byappropriately bending a single strip (FIGS. 5A). A second embodiment(FIG. 7) utilizes a single flat tray with a staggered series ofprogressively larger, grading holes therein in place of the trays withthe V-shaped channels of the first embodiment.

13 Claims, 11 Drawing Figures PATENTEUJAN 8|974 3.784.007

sum 10? 3 PATENTEU JAN 8 I974 SREET 2 0F 3 PATENTED JAN 8 I974 SHEET 3BF 3 FIG. 8A.

1 DYNAMIC SHRIMP GRADER AND GRADING METHOD BACKGROUND OF THE INVENTIONThe present invention relates to a grading machine and method thereoffor grading and separating all types of shrimp including headless orheads-on shrimp, precooked or not, and peeled or not. The presentinvention more particularly relates to a dynamic shrimp grading machine,and a method of grading, which includes an inclined tray or trays whichare moved upwardly and forwardly, driving the shrimp down the trays andgrading 'them according to size by means of either terminal slots orcircular holes, which get progressively larger as the shrimp move downthe machine.

I-Ieretofore, there has been a long standing desire and need in thecommercial shrimp processing industry for a shrimp grader which hasuniversal application'to all types and conditions of shrimp, is highlyaccurate in its grading, is relatively compact, achieves a large numberof size gradings within a short distance, causes no damage to the shrimpwhich are particularly delicate after peeling, and has no real cleaningor jamming problems. All prior shrimp graders suffered from the lack ofone or more of the foregoing desired characteristics, while the presentinvention offers the first real achievement of these goals.

A typical example of a prior art shrimp grader which has been used bythe commercial shrimp processing industry with less than completelysatisfactory results is shown in the U.S. Pat. to Demarest et al. (No.2,964,181, issued Dec. 13, 1960) which use s a series of Archimedes-typescrews positioned above an inclined pan, the distance between each screwand the pan serving to grade the shrimp. The Demarest machine howeversuffers from problems of inaccuracy caused by different size shrimpbecoming intermixed during grading, with smaller shrimp ridingpiggy-back on the larger shrimp being moved by the screws, causing themto be graded out through the wrong slot. Additionally, the Demarestmachine in practice is applicable only to peeled, headless shrimp.

The present invention overcomes all of these prior art deficiencies byproviding a dynamic system which positively moves the shrimp without anydamage down the grading structure and, by its action on the shrimp,causes the shrimp to more properly align itself for grading, and yetachieves this action in a structure which is highly compact, allowing arelatively large number of grading sizes within a relatively short span.This dynamic action is achieved by mounting the grading trays on aseries of reinforced fiberglass-strip springs angularly mounted to thebasic support structure of the grader, the upper tray structure thenbeing eccentrically driven upwardly andforwardly by means of aneccentric motor drive. Universality of application is achieved byutilizing in the grading structure easily interchangeable grading trays,one type being a series of juxtaposed trayshaving a parallel set ofV-shaped channels terminating in grading slots or, alternately, a single, continuous tray having a series of circular grading apeturestherein.

Additional objects and advantages of the present invention will beapparent from an understanding of the details of the structure andmethod of use of the present invention, which will be fully disclosedwith reference to the description of the perferred embodiments belowread in conjunction with the attached drawings which will now be brieflydescribed.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 through 4 are perspective,top, side, and end views, respectively, of a first embodiment of thedynamic shrimp grader of the present invention, FIG. 1 showing headless,unpeeled shrimp being processed; while FIGS. 5 and 6 are endcross-sectional and top views, respectively, of the V-shaped channeltrays used in FIGS. 1-4, the former figure showing some of the channelsof a tray while the latter figure shows only a single channel.

FIG. 5A, similar in perspective to FIG. 5, shows an alternate embodimentof the construction of the V- shaped channels.

FIG. 7 is a perspective view of an alternate embodiment of the gradingtray structure which can be utilized on the grading machine of FIGS. l-4in place of the V- shaped grading trays of the first embodiment.

FIGS. 8A through 8C are side views, partially cut away, of a headless,unpeeled shrimp in one of the V- shaped channels, showing the shrimpstendency to become extended out in more of a straight line rather thanmaintaining its normal full curvature, due to the dynamic action of thetray, as the shrimp progresses down the channel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in FIGS. l-4,the dynamic shrimp grading machine of the present invention includes anupper size grading structure which is mounted on upper frame member 2which is flexibly and movably mounted by means of angularly disposed,reinforced fiberglass springs 5 with respect to the lower frame member 3which in turn is fixedly supported by basic, inverted U- shaped supportlegs 4 with respect to the ground. The upper frame member 2, and hencethe tray grading structure mounted thereon is initially driven upwardlyand forwardly in continuing cycles by means of a reciprocating eccentricdrive.

As seen particularly in FIG. 3, the reciprocating eccentric driveincludes an electric motor 6 which by means of belt 7 drives aneccentric motion producing element 8. The'eccentric 8 through hanger arm9 and connectorhead l0 drives with a general reciprocating actionthe-upper portion of fiberglass spring support 5, which in turn impartsthe dynamic action to the upper frame member 2 utilized in the presentinvention.

wardly before returning to its original position for another cycle. I

Although the structure particularly illustrated and described hereinwith respect to the reciprocating eccentric drive and the mountingstructure between the frame member 2, 3 produces the best embodimentlength of the strip 5, the stroke of the eccentric 8, and

the speed of the motor 6. The resultant motion however must besufficient to align and give a forward irn petus to the shrimp, and yetnot be such as to cause damage to the delicate shrimp meats.

A series of juxtaposed, downwardly inclined, grading trays la-ld arefixedly mounted on the upper frame member 2 by means of a series ofvertical channel iron supports 15.

Each tray 1 (a-d) includes a set of parallel, V-shaped channels 13 eachending in an identically dimensioned grading slot 12, the slot structurebeing shown in close up detail in FIG. 6. The initial portions 14 of thechannels 13 are solid in order to provide a preliminary space upon whichthe shrimp can fall without hitting a grading slot. Were the shrimp tofall directly unto a grading slot, larger shrimp would have a tendencyto become wedged in the slot.

The length as well as the width of the slots 12 is particularlyimportant for the best grading operation of the machine, and the two areinterdependent. As a general rule, all shrimp of a particular thicknesshave substantially the same effective length. Thus all shrimp having athickness of the order of seven-eighths of an inch will have generally alength of 6 inches. For maximum effectiveness the length of the gradingslot 12 should be substantially equal to the effective length of theshrimp whose thickness is identical to the width of that particularslot. Were it to be much greater, some shrimp would have a tendency tojam in the slot even though it was of a size normally to go pass thatslot; and were it substantially shorter, some of the shrimp which shouldhave fallen through the slot, will pass it.

Beneath the grading slots 12 are suspended downwardly inclined,collection and conveying pans l l which are mounted on the lower supportstructure 3 of the machine. The laterally disposed pans 11 serve toseparately collect and convey the graded shrimp out of the gradingmachine for subsequent processing such as packaging. Each pan 11 can bemounted in like fashion on fiberglass strip spring and be dynamicallymoved with respect to the upper frame structure to enhance its conveyingcapability by causing the shrimp to be driven down its surface.

As many grading trays l (a-d) with differing size grading slots 12 canbe provided as desired in view of the ultimate number of separation orgrades needed. A final collecting pan extending longitudinally out ofthe machine is provided at the end of the final tray M in place of theend member 14 to collect all those shrimp which are still too large topass through the slot 12d. The machine will thus produce a total numberof size grade levels equal to the number of grading trays 1 (-11) plusone. Y

The trays l (a-d) are uniform in length and are designed to be easilyremoved from the vertical supports 15 so that the sizing or gradingdimensions produced by the machine can be readily, easily and quicklychanged as desired.

As an alternate embodiment, rather than the series of trays l (a-d) withthe terminal slots 12 as described above. a single tray having a seriesof staggered, progressively larger, circular apertures 112 with a singlechannel '113 is also provided (note P16. 7). Such a tray 101 has beenfound to be particularly effective in grading peeled cooked shrimp andis designed to be mounted on the same vertical supports 15 whichsupported the trays l (a-d). The vertical supports 15 have an additionalset of bolt holes to mate with the corresponding holes in the sides ofthe tray 101 for easy interchangeability of the tray structures. Sucheasy substitution of grading tray structures greatly enhances theflexibility of the grading machine of the present invention and allowsits universality of application to all types and conditions of shrimp.

As best illustrated in FIG. 5, each tray 1 (a-d) can be made up of aseries of, for example, stainless steel or aluminum angle strips 17,connected together by means of angle members 18 which also serve to addstrength and rigidity to the tray structure. Alternately, as illustratedin FIG. 5A, each V-shaped channel can be made of a single strip bentinto the more up-right configuration illustrated. As shown in H0. 5A,the up-right configuration comprises a first, lower, central section 50emanating out from the apex 51 and a second, upper section 52 alsoemanating out but at less an angle than said first section. The angle 52between the walls of said two sections thus are less than The slopingsides of the V-shaped channels 13 serve to centrally and verticallyalign and position the shrimp, regardless of size, for highly accurategrading. Although such has not been found to be necessary, afriction-reducing and easily cleanable surfacing substance such asTeflon can be coated on the working surface of the strips 17.

The eccentrically driven, upper portion of the grading machine providesa very important dynamic action which produces very advantageous anduseful effects on the shrimp as they progress down the machine, greatlyenhancing its size grading accuracy.

The dynamic action of the machine causes the shrimp to have a poweredeffect or dynamic action as it moves down the grading channel 131113).This dynamic action causes the shrimp to become separated from eachother and, in the V-shaped embodiment, insures the near upright orvertical alignment of the shrimp due to the support and guidanceproduced by the sides of the V-shaped channel. The machine thusinherently and accurately aligns the shrimp parallel to the length ofthe grading slot insuring accurate grading Moreover, in the case ofheadless shrimp, the dynamic action of the machine causes the shrimp tounbend to some degree as it moves down the grading channel. This latteraction is illustrated in FIGS. 8A through 8C, although somewhatexaggerated in the figures for illustrative purposes. The morestraightly aligned the shrimp become, the more accurate will be thegrading because of the improved face-to-face contact the shrimp then haswhen it meets the grading Typical Dimensions Dimension Element OverallWidth of Machine 48" Overall Length of Machine 14' Length of Trays la-ld25" Typical Widths of Slots l2a-l2d 5/16; 3/8"; 7/ 16; 9/16" TheRespective Lengths of Slots Ila-12d 4"; 4 /1"; 5"; 5%" Angle ofInclination of Trays la-ld 5 Angle of V-Shaped Channels 13 90 Length ofStrips 5 Width of Strips 5 2" Thickness of Strips 5 V4" Angle ofInclination of Strips 5 (From horizontal) 60 Stroke of Eccentric 8 Speedof Rotation of Eccentric 8 500 RPM Length of Tray 101 14' Method ofOperation The method of operation of the foregoing described machine isas follows.

Processed shrimp, usually coming from a wash tank prior to grading, isconveyed to the top of the shrimp grader and the shrimp to be graded arefed by conveyor down onto the initial solid portion 14 of tray 1a, withthe shrimp being divided as equally as possible between the variouschannels 13. Under the upward, forward and downward motion of the trays,the shrimp begin to progress down the tray 10 in separate, single filefashion, and those shrimp which are small enough to fit through theslots 12a fall down into the collecting and conveying pan 11a. Thelarger shrimp continue to move down the channels 13 of tray 1a untilthey fall down onto the initial portion 14 of juxtaposed tray lb and, inlike fashion, move down trays lb, 1c and 1d until all the shrimp havebeen graded through the slots 12 which are analogous to their width.

The separated and graded shrimp are then conveyed out of the machine bymeans of pans 11 for further processing, including usually a finalinspection and ultimately packaging.

The method of operation when using the alternate tray 101 of FIG. 7 isthe same with the exception that of course there is no dropping from oneset of trays to another, there being only one continuous, downwardlyinclined tray 101. When using the tray 101, the shrimp are gradedaccording to their diameter when laid on their sides. Because tray 101is used with cooked, peeled shrimp, the straightening action of theshrimp as discussed above with respect to FIGS. 8A-8C is not effectivebecause the cooked peeled shrimp curl basically into a circle and lie onsides on the tray v101. This is, of course, as desired when gradingcooked, peeled shrimp.

Because many varying and different embodiments may be made within thescope of the inventive concept herein taught and disclosed, and becausemany modifications may be made in the embodiments herein detailed inaccordance with the descriptive requirements of the law, it is to beunderstood that the details herein are generally speaking to beinterpreted as illustrative only, and not in a limiting sense.

What is claimed as invention is;

l. A dynamic shrimp grading machine for grading shrimp according totheir size comprising:

an upper frame portion;

a basic frame support structure;

mounting means for mounting said upper frame portion to said basic framesupport structure in such a manner as to allow said upper frame portionto be moved at least forwardly and backwardly along the longitudinalaxis of the machine;

drive means for moving said upper portion with respect to said basicframe support structure at least forwardly along the longitudinal axisof the machine and then cyclically and continuously repeating itself;and

tray grading means mounted on said upper frame portion for grading andseparating the shrimp according to size, said tray grading meansincluding a series of size-grading apertures therein which progressivelyget larger as said tray grading means is progressed, said tray gradingmeans including a series of adjacent, juxtaposed inclined trays, eachcomprising a series of elongated channels, each of said channels havinga substantial, extended, initial portion which is solid and an endportion which tcrminates in a grading slot of uniform width, said solidportion serving as a non-grading portion upon which the shrimp can fallor be moved and said slot serving as said size-grading aperture; wherebyshrimp placed on the top of said grading tray means are dynamicallymoved down said grading tray means and are separated and gradedaccording to size by the smaller ones falling through the earlierencountered grading apertures and the larger shrimp falling through thelarger grading apertures as the shrimp progress down said grading traymeans.

2. The dynamic shrimp grading machine of claim 1 wherein said mountingmeans further allows an initially upward motion along with the forwardmotion to cause the shrimp to have a hippity-hop action as they progressthrough the machine. I

3. The dynamic shrimp grading machine of claim 1 wherein said traygrading means is one continuous, inclined pan having a series ofcircular apertures therein of progressively larger diameter throughoutsubstantially all of its length.

4. The dynamic shrimp grading machine of claim 1 wherein said mountingmeans comprise a series of angularly disposed, elastic strips, thetermination portions of which are attached to said basic frame supportstructure and said upper frame portion.

5. The dynamic shrimp grading machine of claim 1 wherein said drivemeans includes the following:

source of rotary motive power; eccentric drive means for changing thecircular rotary motion to reciprocating eccentric motion;

drive means for feeding the rotary motion of said soruce of motive powerto said eccentric drive means; and

connector rod drive means for transmitting the reciprocating eccentricmotion produced by said eccen-' tric drive means to said upper frameportion.'

6. The dynamic shrimp grading machine of claim 1 wherein said endportion of each of said trays is physically removed from said initialportion of the succeeding tray, each of said trays being higher than andoverlaping the succeeding one.

7. The dynamic shrimp grading machine of claim 6 wherein each of saidchannels has a V-shaped crosssection, the walls of said channel freelysupporting the shrimp in an upright position for enhanced gradingaccuracy.

8. The dynamic shrimp grading machine of claim 7 wherein said walls havetwo sections, an upper and a lower, the wall segments of said lowersection converging to the apex of the V-shaped cross-section andemanating out therefrom to join with the wall segments of said uppersection, the wall segments of said upper section likewise emanating outbut at a less angle than said first section, the angle between the wallsegments of said upper and lower sections having less than a 180 anglebetween them.

9. The method of grading shrimp according to their size comprising thefollowing steps:

a. providing a grading structure comprising an upper frame portion;

a basic frame support structure;

mounting means for mounting said upper frame portion to said basic framesupport structure in such a manner as to allow said upper frame portionto be moved at least forwardly and backwardly along the longitudinalaxis of the machine;

drive means for moving said upper portion with respect to said basicframe support structure at least forwardly along the longitudinal axisof the machine and then cyclically and continuously repeating itself;

tray grading means mounted on said upper frame portion for grading andseparating the shrimp according to size, said tray grading meansincluding a series of size-grading apertures therein which progressivelyget larger as said tray grading means is progressed; whereby shrimpplaced on the top of said grading tray means are dynamically moved downsaid grading tray means and are separated and graded according to sizeby the smaller ones falling through the earlier encountered gradingapertures and the larger shrimp falling through the larger gradingapertures as the shrimp progress down said grading tray means;

b. dumping shrimp unto the top of said tray grading 7 means;

0. moving said upper frame portion initially in an upwardly direction toa limited extent and then forwardly to thereby positively anddynamically drive the shrimp down the grading tray means;

d. continuously repeating the movement of step c until the shrimp haveeither fully progressed the grading tray means or have fallen throughsaid grading apertures; and

e. collecting the shrimp from under said grading apertures and conveyingthem out of the machine for further processing.

10. The method of claim 9 wherein in moving said upper frame portion,the shrimp are driven so that they follow a hippity-hop" action as theyprogress down said grading tray means.

11. The method of claim 10 wherein, in driving said upper frame portionupwardly and forwardly, the shrimp are driven so that they have atendency to unbend to some degree away from their normally curleddisposition.

12. A dynamic shrimp grading machine for grading shrimp according totheir size comprising:

an upper frame portion;

a basic frame support structure;

mounting means for mounting said upper frame to said basic frame supportstructure in such a manner as to allow said upper frame portion to bemoved at least forwardly and backwardly;

drive means for moving. said upper portion with respect to said basicframe support structure at least forwardly along the longitudinal axisof the machine and then cyclically and continuously repeating itself;

tray grading means mounting on said upper frame for grading andseparating the shrimp according to size, said tray grading meansincluding a series of size-grading apertures therein which progressivelyget larger as said tray grading means is progressed; whereby shrimpplaced on top of said tray grading means are dynamically driven downsaid tray grading means and are separated and graded according to sizeby the smaller ones falling through the earlier encountered gradingapertures and the larger shrimp falling through the larger gradingapertures as the shrimp progress down said tray grading means;

said tray grading means including a series of adjacent, juxtaposedinclined trays, each comprising a series of elongated channels, each ofsaid channels having an initial portion which is solid and an endportion which terminates in a grading slot of uniform width, said slothaving a length being approximately equal to the length of the shrimphaving a thickness substantially equal to said width, said slot servingas said size-grading aperture.

13. A shrimp grading machine for grading shrimp according to their sizecomprising:

an upper frame portion;

a basic frame support structure;

mounting means for mounting said upper frame to said basic frame supportstructure;

tray grading means mounting on said upper frame for grading andseparating the shrimp according to size, said tray grading meansincluding a series of size-grading apertures therein which progressivelyget larger as said tray grading means is progressed, said tray gradingmeans including a series of inclined, elongated channel sections, eachof said channel sections having an initial portion which is solid and anending portion which terminates in a grading slot of uniform width, saidslot having a length which is interdependent with the width of the slot,the length being approximately equal to the length of the shrimp havinga thickness substantially equal to said width, said slots serving assaid size-grading aperture; and

means for moving the shrimp down said channel sections; whereby shrimpmove down said tray grading means and are separated and graded accordingto size by the smaller ones falling through the earlier encounteredgrading apertures and the larger shrimp falling through the largergrading apertures as the shrimp progress down said tray grading

1. A dynamic shrimp grading machine for grading shrimp according totheir size comprising: an upper frame portion; a basic frame supportstructure; mounting means for mounting said upper frame portion to saidbasic frame support structure in such a manner as to allow said upperframe portion to be moved at least forwardly and backwardly along thelongitudinal axis of the machine; drive means for moving said upperportion with respect to said basic frame support structure at leastforwardly along the longitudinal axis of the machine and then cyclicallyand continuously repeating itself; and tray grading means mounted onsaid upper frame portion for grading and separating the shrimp accordingto size, said tray grading means including a series of size-gradingapertures therein which progressively get larger as said tray gradingmeans is progressed, said tray grading means including a series ofadjacent, juxtaposed inclined trays, each comprising a series ofelongated channels, each of said channels having a substantial,extended, initial portion which is solid and an end portion whichterminates in a grading slot of uniform width, said solid portionserving as a non-grading portion upon which the shrimp can fall or bemoved and said slot serving as said size-grading aperture; wherebyshrimp placed on the top of said grading tray means are dynamicallymoved down said grading traY means and are separated and gradedaccording to size by the smaller ones falling through the earlierencountered grading apertures and the larger shrimp falling through thelarger grading apertures as the shrimp progress down said grading traymeans.
 2. The dynamic shrimp grading machine of claim 1 wherein saidmounting means further allows an initially upward motion along with theforward motion to cause the shrimp to have a ''''hippity-hop'''' actionas they progress through the machine.
 3. The dynamic shrimp gradingmachine of claim 1 wherein said tray grading means is one continuous,inclined pan having a series of circular apertures therein ofprogressively larger diameter throughout substantially all of itslength.
 4. The dynamic shrimp grading machine of claim 1 wherein saidmounting means comprise a series of angularly disposed, elastic strips,the termination portions of which are attached to said basic framesupport structure and said upper frame portion.
 5. The dynamic shrimpgrading machine of claim 1 wherein said drive means includes thefollowing: source of rotary motive power; eccentric drive means forchanging the circular rotary motion to reciprocating eccentric motion;drive means for feeding the rotary motion of said soruce of motive powerto said eccentric drive means; and connector rod drive means fortransmitting the reciprocating eccentric motion produced by saideccentric drive means to said upper frame portion.
 6. The dynamic shrimpgrading machine of claim 1 wherein said end portion of each of saidtrays is physically removed from said initial portion of the succeedingtray, each of said trays being higher than and over-laping thesucceeding one.
 7. The dynamic shrimp grading machine of claim 6 whereineach of said channels has a V-shaped cross-section, the walls of saidchannel freely supporting the shrimp in an upright position for enhancedgrading accuracy.
 8. The dynamic shrimp grading machine of claim 7wherein said walls have two sections, an upper and a lower, the wallsegments of said lower section converging to the apex of the V-shapedcross-section and emanating out therefrom to join with the wall segmentsof said upper section, the wall segments of said upper section likewiseemanating out but at a less angle than said first section, the anglebetween the wall segments of said upper and lower sections having lessthan a 180* angle between them.
 9. The method of grading shrimpaccording to their size comprising the following steps: a. providing agrading structure comprising an upper frame portion; a basic framesupport structure; mounting means for mounting said upper frame portionto said basic frame support structure in such a manner as to allow saidupper frame portion to be moved at least forwardly and backwardly alongthe longitudinal axis of the machine; drive means for moving said upperportion with respect to said basic frame support structure at leastforwardly along the longitudinal axis of the machine and then cyclicallyand continuously repeating itself; tray grading means mounted on saidupper frame portion for grading and separating the shrimp according tosize, said tray grading means including a series of size-gradingapertures therein which progressively get larger as said tray gradingmeans is progressed; whereby shrimp placed on the top of said gradingtray means are dynamically moved down said grading tray means and areseparated and graded according to size by the smaller ones fallingthrough the earlier encountered grading apertures and the larger shrimpfalling through the larger grading apertures as the shrimp progress downsaid grading tray means; b. dumping shrimp unto the top of said traygrading means; c. moving said upper frame portion initially in anupwardly direction to a limited extent and then forwardly to therebypositively and dynamically drive the shrimp down the grading tray means;D. continuously repeating the movement of step c until the shrimp haveeither fully progressed the grading tray means or have fallen throughsaid grading apertures; and e. collecting the shrimp from under saidgrading apertures and conveying them out of the machine for furtherprocessing.
 10. The method of claim 9 wherein in moving said upper frameportion, the shrimp are driven so that they follow a ''''hippity-hop''''action as they progress down said grading tray means.
 11. The method ofclaim 10 wherein, in driving said upper frame portion upwardly andforwardly, the shrimp are driven so that they have a tendency to unbendto some degree away from their normally curled disposition.
 12. Adynamic shrimp grading machine for grading shrimp according to theirsize comprising: an upper frame portion; a basic frame supportstructure; mounting means for mounting said upper frame to said basicframe support structure in such a manner as to allow said upper frameportion to be moved at least forwardly and backwardly; drive means formoving said upper portion with respect to said basic frame supportstructure at least forwardly along the longitudinal axis of the machineand then cyclically and continuously repeating itself; tray gradingmeans mounting on said upper frame for grading and separating the shrimpaccording to size, said tray grading means including a series ofsize-grading apertures therein which progressively get larger as saidtray grading means is progressed; whereby shrimp placed on top of saidtray grading means are dynamically driven down said tray grading meansand are separated and graded according to size by the smaller onesfalling through the earlier encountered grading apertures and the largershrimp falling through the larger grading apertures as the shrimpprogress down said tray grading means; said tray grading means includinga series of adjacent, juxtaposed inclined trays, each comprising aseries of elongated channels, each of said channels having an initialportion which is solid and an end portion which terminates in a gradingslot of uniform width, said slot having a length being approximatelyequal to the length of the shrimp having a thickness substantially equalto said width, said slot serving as said size-grading aperture.
 13. Ashrimp grading machine for grading shrimp according to their sizecomprising: an upper frame portion; a basic frame support structure;mounting means for mounting said upper frame to said basic frame supportstructure; tray grading means mounting on said upper frame for gradingand separating the shrimp according to size, said tray grading meansincluding a series of size-grading apertures therein which progressivelyget larger as said tray grading means is progressed, said tray gradingmeans including a series of inclined, elongated channel sections, eachof said channel sections having an initial portion which is solid and anending portion which terminates in a grading slot of uniform width, saidslot having a length which is interdependent with the width of the slot,the length being approximately equal to the length of the shrimp havinga thickness substantially equal to said width, said slots serving assaid size-grading aperture; and means for moving the shrimp down saidchannel sections; whereby shrimp move down said tray grading means andare separated and graded according to size by the smaller ones fallingthrough the earlier encountered grading apertures and the larger shrimpfalling through the larger grading apertures as the shrimp progress downsaid tray grading means.